Electron gun for cathode ray tubes



May 17, 1966 E. GUNDERT ETAL ELECTRON GUN FOR CATHODE RAY TUBES Filed Nov. 28, 1960 INVENTORSI EBERHARD GUNDERT PAUL BERGER m a H.

U K N mm R B O E R A WE AH G T United States Patent Filed Nov. 28, 1960, Ser. No. 71,988

3 Claims. (Cl. 313-82) The invention refers to an electron gun for cathode ray tubes consisting of a first and a second electrode assembly the latter of which is already pre-assembled to the first one.

It has been suggested before to employ for the electron gun of the cathode ray tubes the same construction of mounting the electrodes between two mica plates as used in the radio tubes. In such an arrangement the cathode, the control grid, and two mounting brackets are assembled insulated between mica discs. This preassembled electrode unit is mounted to the screen grid and the remainder of the electrodes, which are combined to a second electrode assembly in such a manner that the holder of the first unit has been welded to a mounting plate attached to a screen grid. However, it has been found that for such a proposed arrangement it is difficult to combine these two preassembled electrode assemblies in such a manner that they meet the electron-optical requirements. Since for this proposed arrangement the control grid contains an opening to allow the beam to pass, it is absolutely mandatory that during the assembly of the two electrode units these beam openings are centered exactly with the other beam openings of the screen grid and the other electrodes. The disadvantage of this previously proposed arrangement consist in the difficulty of the exact assembly of the two preassembled electrode units.

Furthermore, it has been proposed for the purpose of increasing the sensitivity of a cathode ray tube to place a parallel wire grid before the beam opening of the control electrode. By proper placement of the grid wires in relation to the screen, it is possible to focus the beam on the screen for one deflection more than in the other one. Therefore, it is possible to obtain a sharply focussed beam in the direction of the horizontal lines. In this case a blurred light spot would be objectionable while at right angles to the horizontal lines a decreased sharpness is permissible since the line structure of the picture will be slightly wiped out. Furthermore, this control grid achieves an increased sensitivity of the tube, as mentioned before.

An object of the invention is to achieve the construction of an electron gun that possesses the above mentioned disadvantages only to a slight degree or not at all.

According to the invention it is proposed that the second electrode assembly shall consist of at least two electrodes with no openings encompassing the beam.

Using the examples shown in the illustration, the invention is explained as follows:

FIGURE 1 shows the cross section of a part of the standard electron gun which has the electrodes fastened to glass rods 2 by means of brackets 1. For example, the electrode 3 shall represent a screen grid electrode and the electrode 4 a control grid. These two electrodes, to which additional electrodes may be added, are attached to the insulating rods 2 by means of brackets 1 and contain openings 9 and encompassing the beam. A second electrode unit, consisting of preassembled mica plates 5, cathode 6 and grid '8 wound on rods 7 is fastened to the control grid 4.

FIGURE 2 is a section taken through FIG. 1 at line 2-2.

It is of special importance that the second electrode assembly consists of electrodes which do not have openings encompassing the beam. Thus, when mounting the second electrode unit to the other electrode unit only the distance in the beam direction must be checked, while the sideway displacements of the cathode and the grid due to usual tolerances-may be disregarded. This is due to the fact that the grid possesses a width, respectively cathode 6 is covered with emission paste to such a width that in any case the beam opening 9 in the control grid 4 will be completely covered by the grid 8 respectively cathode 6. The centering of the beam opening 9 to the beam opening 10 as Well as the beam openings of other electrodes fastened to the glass rods 2 has been performed before the assembly of the second electrode unit. This operation can be easily accomplished by means of a centering rod due to the absence of the second electrode assembly. Since at the above described eXample grid 8, rods 7 and electrode 4 shall possess the same potential, the simplest mounting method of the second unit to the first consists of welding rods 7, supporting the grid, direct to the bracket lobe 11 of the control grid 4. The heater 12 protrudes at one side of the cathode tube, while the complete cathode assembly is surrounded by a screen 13.

The cross construction of the cathode has the advantage of a small length in axial direction of the tube and furthermore the distances grid-cathode can be easily controlled in this proven construction. A special advantage of this invention is the fact that the second electrode unit does not have to be exactly adjusted, radially, that is in a direction sideways to the remainder of the electrodes.

Rather it is sufiicient to use a simplified alignment of the two units for the mounting of the two electrode units, as shown in the given example by having the mica plates protrude through the slot 14 in the control grid 4.

What we claim as new and desire tosecure by Letters Patent of the United States is:

1. An electron gun for a cathode ray tube, said elec tron gun comprising a first electrode assembly including first and second electrodes, each electrode having a surface disposed transverse to a reference axis and provided with a central coaxial opening for passing an electron beam, said first and second electrodes being carried by a pair of insulating mount members in coaxial alignment, a second electrode assembly including a pair of support members of electrically insulating material carried by said first electrode, an emitter electrode carried by said insulating support members in confronting spaced relationship with said coaxial opening, a pair of grid support members extending between said insulating support members and carried by said first electrode, said grid support members being disposed on opposite sides of said emitter electrode in a plane generally transverse to said reference axis, and a plurality of spaced grid wires extending between said grid support members in a plane situated between said emitter electrode and said first electrode, said gridwires being electrically connected to and at the same potential as said first electrode.

2. An electron gun for a cathode ray tube, said electron gun comprising a first electrode assembly including first and second electrodes, each electrode having a surface disposed transverse to a reference axis and provided with a central coaxial opening for passing an electron beam, said first and second electrodes being carried by a pair of insulating mount members in coaxial alignment, a second electrode assembly including a pair of support members of electrically insulating material carried by said first electrode, a cathode electrode carried by said insulating support members and having an emitting surface extending transversely to said reference axis in confronting spaced relationship .with said coaxial opening, a pair of relatively stiff grid support rods extending between said Patented May 17, 1966 insulating support members and directly electrically connected to and carried by said first electrode, said grid support rods being disposed on transversely opposite sides of said cathode with the surfaces of said rods facing said first electrode defining a plane generally transverse to said reference axis and spaced between said cathode and said first electrode aperture, and a plurality of spaced relatively fine grid wires stretched between said g-rid support rods in a plane situated between said cathode and said first electrode.

3. An electron gun for a cathode ray tube, said electron gun comprising a first electrode assembly including first and second electrodes, each electrode having a surface disposed transverse to a reference axis and provided with a central coaxial opening for passing an electron beam, said first electrode further being provided with extending bracket lobes and said first and second electrodes being carried by a pair of insulating mount members in coaxial alignment, a second electrode assembly including a pair of support members of electrically insulating material carried by said first electrode, a sleeve-shaped cathode electrode supported by said insulating support members and extending transversely to said reference axis in confronting spaced relationship with said coaxial opening,

facing said first electrode, a pair of grid support rods extending between said insulating support members and carried by said bracket lobes, said grid support rods being disposed on transversely opposite sides of said cathode with the surfaces of said rods facing said first electrode defining a plane generally transverse to said reference axis and spaced between said cathode and said first electrode aperture, and a plurality of spaced turns of grid wire wound on said grid support rods with a portion of each turn situated between and spaced from said cathode and said first electrode.

References Cited by the Examiner UNITED STATES PATENTS 2,490,008 11/1949 Shulrnan 313-432 X 2,813,215 11/1957 Reichert. 2,867,687 1/1959 Glenn. 3,065,368 11/ 1962 Atti 3l3-82 FOREIGN PATENTS 1,195,970 5/1959 France;

812,089 4/ 1959 Great Britain.

a coating of electron emission material on said cathode 25 GEORGE WESTB'YPHmary Examiner RALPH G. NILSON, Examiner. 

1. AN ELECTRON GUN FOR A CATHODE RAY TUBE, SAID ELECTRON GUN COMPRISING A FIRST ELECTRODE ASSEMBLY INCLUDING FIRST AND SECOND ELECTRODES, EACH ELECTRODE HAVING A SURFACE DISPOSED TRANSVERSE TO A REFERENCE AXIS AND PROVIDED WITH A CENTRAL COAXIAL OPENING FOR PASSING AN ELECTRON BEAM, SAID FIRST AND SECOND ELECTRODES BEING CARRIED BY A PAIR OF INSULATING MOUNT MEMBERS IN COAXIAL ALIGNMENT, A SECOND ELECTRODE ASSEMBLY INCLUDING A PAIR OF SUPPORT MEMEBRS OF ELECTRICALLY INSULATING MATERIAL CARRIED BY SAID FIRST ELECTRODE, AN EMITTER ELECTRODE CARRIED BY SAID INSULATING SUPPORT MEMBERS IN CONFRONTING SPACED RELATIONSHIP WITH SAID COAXIAL OPENING, A PAIR OF GRID SUPPORT MEMBRS EXTENDING BETWEEN SAID INSULATING SUPPORT MEMBERS AND CARRIED BY SAID FIRST ELECTRODE, SAID GRID SUPPORT MEMBERS BEING DISPOSED ON OPPOSITE SIDES OF SAID EMITTER ELECTRODE IN A PLANE GENERALLY TRANSVERSE TO SAID REFERENCE AXIS, AND A PLURALITY OF SPACED GRID WIRES EXTENDING BETWEEN SAID GRID SUPPORT MEMBERS IN A PLANE SITUATED BETWEEN SAID EMITTER ELECTRODE AND SAID FIRST ELECTRODE, SAID GRID WIRES BEING ELECTRICALLY CONNECTED TO AND AT THE SAME POTENTIAL AS SAID FIRST ELECTRODE. 